The present invention relates to a device for transmitting signals to one or a plurality of circuit modules integrated in a head restraint of a motor vehicle seat.
In order to further improve the protection afforded motor vehicle passengers in the event of accidents, the restraint systems in motor vehicles are becoming more and more complex. Among the expressions of this is the fact that in the head restraints of motor vehicle seats airbags are installed that are specially designed to offer protection in the head and neck area of vehicle passengers. Along with the airbags, the driver stages required for triggering them (a firing element having control electronics) need to be integrated in the head restraints. These driver stages are usually driven from a central control unit in the vehicle. Between the control unit and the driver stage integrated in a head restraint, signals are transmitted in both directions. For example, in the event of a collision, a triggering signal is transmitted from the control unit to the driver stage, or diagnostic signals of the driver stage, which must constantly be monitored for its performance reliability, are conveyed to the control unit. If the driver stage contains circuit modules that must be supplied with current, the necessary energy must also be transmitted from the control unit to the driver stage. Similarly, in a head restraint it is possible to integrate a sensor which performs a seat occupancy detection using ultrasound or optical or electromagnetic waves.
Since the head restraint is a movable part and therefore the circuit modules integrated in it do not have a constantly fixed position with respect to the control unit, the signal transmissions are not carried out using fixed conductor connections. Therefore, the present invention is based on the objective of indicating a device for transmitting signals to one or a plurality of circuit modules integrated in the head restraint of a motor vehicle seat, circuit modules that can operate without transmission means that are subject to wear.
The aforementioned objective is achieved through the fact that the signal transmission takes place via at least one induction coil arranged in the seat back of the vehicle seat and via one or both head restraint guide rod/rods, which are interactively coupled to the at least one coil and are movably supported in the seat back. This device represents a contact-free signal connection to one or a plurality of circuit modules in a head restraint, sliding-action contacts or cable connections, both subject to wear, not being necessary. As a result of the fact that the guide rods of the head restraint are integrated into the signal transmission, the expense for the transmission device is significantly reduced. The device is composed of a small number of separate parts, which makes assembly easier.
According of the present invention proceed from the subclaims. According to them, at least one of the two guide rods can be wrapped around by a secondary coil, which, along with the at least one primary coil in the seat back, constitutes a transmitter (repeating coil), the secondary coil being wound on the guide rod so as to be distributed over a length, such that in every position of the head restraint an inductive coupling exists between the coils. The secondary coil on the guide rod is advantageously surrounded by an insulating sleeve. The primary coil coaxially surrounds the guide rod carrying the secondary coil and rests in a ring core having a U-shaped cross-section, which concentrates the magnetic flux on the secondary coil.
In a further advantageous embodiment, the two guide rods are electrically connected to each other at their ends in the head restraint and in the seat back, so that as a result a conductor loop arises, in which a current is induced as a result of the at least one coil arranged in the seat back. In the head restraint, elements are provided by which the induced current can be decoupled from the conductor loop. These elements, for example, can be composed of a resistor inserted into the conductor loop or a coil coupled to the conductor loop.
In accordance with a further advantageous exemplary embodiment, the two guide rods are made of a ferromagnetic material, and they are joined to make a magnetic circuit by ferromagnetic connecting pieces present in the head restraint and in the seat back. In the head restraint, a winding is present which is coupled to the magnetic circuit.
A circuit module integrated in the head restraint, for example, can be a driver stage or a seat-occupancy sensor.